Help please with stepper driver step buffer

Greetings All, I'm trying to build a stepper motor driven indexer. The goal is to use the inherent accuracy of a stepper motor and encoder to index a wheel. US Digital sells an IC that uses the output from an encoder to generate step and direction pulses. These pulses can then be used with a stepper motor driver IC to drive a stepper motor. It works well until the stepper motor recieves pulses faster than it can move and steps are lost. If it's easy enough, and cheap enough, I would like to build some type of buffer that will accept the signals from either an encoder or the step and direction IC and output them at a certain rate that doesn't exceed the stepper motor's maximum step rate. Is this something that can be easily done by someone who is good at following directions, can solder well, but really doesn't know much about electronics? Any help would be great. Thanks, Eric R Snow

Reply to
Eric R Snow
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The obvious answer is, slow down the pulses you're sending to the stepper.

How are you generating them now?

Thanks, Rich

Reply to
Rich Grise

The IC that generates the step and direction recieves the output from an encoder that is spun by hand. So what happens is that since the encoder divides each revolution into discrete steps these discrete steps can then be used to index a disc, driven by a stepper motor. If the person turning the encoder too fast spins it too fast steps may be lost. I could somehow limit the speed at which the encoder can be spun, but would rather buffer the signals somehow in order to have an easily spun encoder, with 100 detented positions. Eric

Reply to
Eric R Snow

Then you'll need some kind of FIFO - when the step rate from the knob gets faster than the stepper motor can take, store up the steps, and clock them out at whatever rate the motor can handle. Actually, it sounds like kind of a fun project - I've driven steppers with a Z80, and I've written a FIFO with an 8748 or so - if you have a micro development system, it's just software. ;-)

You _could_ do a hardware FIFO, but it'd be a nightmare, unless you have a CPLD/FPGA development system. ;-)

Good Luck! Rich

Reply to
Rich Grise

Thanks Rich, I was hoping for a single IC solution. It looks like I'll have to limit the speed mechanically. Maybe. The ultimate goal is to come up with a design that amateur machinists can make. The cost needs to be low and the electronics need to be simple. I'm not averse to using a microcontroller myself but if I went this route I'd have to supply pre-programmed microcontrollers. I just want to publish the info and make it available for free non-commercial use. There are many hobby machinists who are retired and have limited incomes. They also, as a group, tend to not be real familiar with more than basic electronics. So I need to be able to provide them with good instructions and a parts list with common devices. In other words, directions suitable for me. There is one option that I've considered and that's position feed back from the stepper motor. This would require another encoder, LED display, and another IC. But as long as the counts from the manually turned encoder match the counts from the stepper motor all is well. Another option is to use the Z pulse from the encoder and a cam operated switch on the stepper shaft to turn on a couple LEDs. This would only verify position once every revolution. But it's the high count indexing where people will be in a hurry so it may be the best option. Eric

Reply to
Eric R Snow

Well, you could build a board with some micro on it, and preprogram each one, for an investment of a few hundred dollars and a lot of your time to program the thing, and just sell it turnkey.

For positional feedback, I'd seriously recommend linear encoders on the bed itself - it totally eliminates slop. :-)

What is it overall you're trying to accomplish?

Thanks, Rich

Reply to
Rich Grise

only single IC solution I can think of is some sort of microcontroller that track the position of the input and dose its best top put the output in the same place as fast as it can.

I know there are some micros that can be just hooked up to a USB port (etc) to program them.

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   Jasen
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Reply to
jasen

Rich, A rotary indexer. Use might be indexing a dial in order to engrave equally spaced lines. Another use could be drilling a hole pattern. With a powerful enough stepper it could even be used for milling arcs. But the main point is that the high accuracy that the encoders and steppers are made to enables precision indexing. The discrete steps would be very useful for indexing gears when milling them. And this high accuracy is available for cheap. The electronics in between the encoder and stepper need to be cheap too. ERS

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Eric R Snow

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